Method of generating steam in a forced flow steam generator



P. PROFOS 2,907,305 METHOD OF GENERATING STEAM IN A FORCED FLOW STEAM GENERATOR Oct. 6, 1959 Filed 001;. 20, 1954 INVENTOR.

RqUL PROF'OS.

BY f d ATTORNEK United States Patent Q METHOD OF GENERATING STEAM IN A FORCED FLOW STEAM GENERATOR Paul Profos, Winterthur, Switzerland, assignor to Sulzer 'Freres, Socit Anonyme, Winterthur, Switzerland, a

corporation of Switzerland Application October 20, 1954, Serial No. 463,469 Claims priority, application Switzerland October 27, 1953 '1 Claim. (Cl. 122-379) The present invention relates to a method for generating steam in and for removing salt from the operating medium of a forced flow steam generator, particularly such operated at supercritical pressure, in which at least a part of the salts contained in the operating medium is deposited on the heating surface of the portion of the steam generator in which the water is converted into steam.

It is an object of the invention to provide a method for removing salts separated from the operating medium of a forced flow steam generator and adhering to the heating surface of the zone of the steam generator in which the water is converted into steam, by periodically washing the deposited salts away from the heating surface by means of a washing agent, without interrupting the operation of the steam generator; during the washing periods the operating medium of the steam generator is bypassed around the zone of the generator in which the water is converted into steam. It may be advisable to deposit the salts contained in the feed water of the steam generator in two separate zones in which the water is converted into steam and to maintain steam generation and deposition of salts in one zone while the other zone is being washed out. The operating medium of the steam generator is preferably diverted from the circuit and used as washing agent. The operating medium which is used for washing out deposited salts is preferably taken from the economizer of the steam generator. As a modification, a washing agent may be introduced from the outside into the zone of the steam generator in which the water is converted into steam and in which salts originally contained in the feed water are deposited.

In a steam generator operating at supercritical pressure, the operating medium is either in the liquid or in the gas phase, and salts carried along by the water do not remain in the liquid phase of the operating medium, as is the case in a steam boiler which is operated below the critical pressure. Therefore, a conventional water separator cannot be used for removing the salts in a supercritical pressure forced circulation steam generator. Since a considerable portion of the salts contained in the feed water of a supercritical pressure steam generator is deposited on the heating surfaces of the zone of the generator in which the water is converted into steam, the salts can be efiiciently removed in such a steam generator. It is only necessary to arrange the zone in which the water is converted into steam and in which the salts are separated in a place where there is no danger of overheating the heating surfaces. The portion of the heating surfaces of the steam generator in which the operating medium reaches the critical point, or rather the critical temperature, and in which the salt is separated may be heated separately, the deposited salts being washed away at suitable intervals. With conventional methods, steam generation is interrupted during the Washing-out periods, the operating medium of the conventional steam generators being pumped as washing liquid through the entire boiler plant until the washing-out of the zone in which water is .normally converted into steam is completed. The con- 2,9073% Patented Oct. 6, 1959 'plants, but which is not possible in large steam generating plants as they are being used in modern power stations.

It is an object of the present invention to provide a method which avoids the aforesaid difficulties and in which the salts deposited on the heating surface of the conversion zone are washed away by means of a washing agent without interrupting normal operation of the steam generator, the operating medium of the generator bypassing the conversion zone. Steam generation is therefore maintained also during the washing-out periods.

The novel features which are considered characteristic of the invention are set forth with particularly in the appended claim. The invention itself however and additional objects and advantages thereof willbest be understood from the following description of embodiments thereof when read in conjunction with the accompanying drawing in which- I Fig. 1 is a diagrammatic illustration of the pipe connections for performing the method according to the invention in a steam generator having one conversion zone in which water is converted into steam;

Fig. 2 diagrammatically illustrates a modified piping arrangement for performing a modified form of the method modified washing-out method according to the invention,

Fig. 5 is a diagram illustrating a steam generator in which the conversion zone is heated by combustion gases and which is adapted for performing the washing-out method according to the invention.

The same numerals designate the same parts in all figures.

As shown in Fig. l, the liquid operating medium is fed by a pump 1 into a preheater 2 and from there through a conduit 3 into a heat exchanger 4, in which the working medium is converted into steam. From the heat exchanger 4, the working medium which is now in the steam phase flows through a conduit 5 and a multipath valve 6 to a superheater 7. The steam, which has been superheated in the superheater 7, is conducted through a conduit 9 to the heat exchanger 4, where the superheated steam indirectly heats the already pre heated Working medium to supercritical temperature. During this process, the salts contained in the working medium precipitate onto the heating surfaces of the heat exchanger. The heating steam leaves the heat exchanger 4 through a conduit 10 and is conducted through a final superheater 11 and therefrom to steam consumers, not shown. The preheater or economizer 2 and the two superheaters 7 and 11 may be heated by combustion gases.

When the separation of the salts in the heat exchanger has progressed so far as to necessitate the washing out of the salts, the multi-path valve 6 is switched to a bypass conduit 8 for detouring a part of the working medium around the heat exchanger 4 and the conduit 5. The by-passed part of the working medium flows. directly from the preheater 2 through the conduit 8 to the superheater 7 where it is converted into steam and proceeds through a connecting conduit 13 provided with generator thus proceeds without interruption, while the separation of the salts from the working medium is temporarily interrupted until the salts which have been eparated in the conversion zone of the heat exchanger have been washed out and removed from the conversion zone. For removing the washed-out salt, a blow-down conduit 14 fitted with a blow-down valve is connected to the conduit 5, between the heat exchanger 4 and the multi-path valve 6. By suitable adjustment of valves 6 and 15, a portion of the working medium supplied by the pump 1 is conducted through the heat exchanger 4 for dissolving the salts deposited in the heat exchanger, carrying them along and removing them through the conduit 14. When desludging of the heat exchanger 4 is completed, the multi-path valve 6 is readjusted and the valves 12 and 15 are closed, so that the working medium again flows through the conversion zone in the heat exchanger 4, for desalting and converting the operating medium into steam, valves 21 and 22 being-open during normal operation of the steam generator.

Since the time needed for desludging is relatively short, there is no danger of accumulation of considerable salt deposits in the superheater 7, in which the operating medium is converted into steam, as long as the heat exchanger 4 is being desludged, particularly if the heat supply to the superheater is suitably controlled. The multipath valve 6 may be replaced by other conventional valves which may be interposed in the individual pipe lines.

Fig. 2 illustrates a modification of the steam generating plant shown in Fig. l. The conduits 3 and 5 connected to the heat exchanger 4 in which the water is converted into steam can be closed by means of valves 16 and 17, respectively. The by-pass conduit 8 of the heat exchanger is equipped with a valve 18. The heat exchanger 4 is supplied with heating medium through conduits 9 and 10. The washing agent for removing deposited salts from the heat exchanger 4 is supplied from a reservoir 23 by means of a pump 24 through a conduit provided with a valve 19 and is removed through a conduit 14 provided with a valve 15. Whereas in the embodiment illustrated in Fig. l the washing agent is taken from a suitable point of the preheater or economizer 2, in the embodiment shown in Fig. 2 a washing agent is used which may be taken from another suitable point of the circuit of the operating medium. A washing agent may be used which is not taken from the operating medium circuit of the steam generator, but from an outside source. It is of advantage to use as highly as possible preheated water for washing and desludging, so that the heat exchanger is not unnecessarily cooled.

Fig. 3 illustrates a steam generating plant in which the salts contained in the operating medium are separated in two individual conversion zones in which water is converted into steam. By suitable switching manoeuvers deposition of salt can be efiected in one of the conversion zones, while the salts previously deposited in the other conversion zone are washed out, so that operation of the steam generator with desalted operating medium is not interrupted. If, for example, the heating surfaces of the heat exchanger 34 which is heated by a heating medium supplied through conduits 39 and provided with valves 51 and 52, respectively, and on which heating surfaces a suificient amount of salt has been deposited, must be desludged, the valves 51 and 52 as Well as the valve 47 in the discharge conduit 35 of the heat exchanger 34 are closed. A blowdown valve in a conduit 44 connected to the conduit 35 between the heat exchanger 34 and the valve 47 is suitably opened, and a valve 46 in the inlet conduit 33 of the heat exchanger 34 is so adjusted that a suflicient amount of water is passed through the heat exchanger 34 from the economizer 32 to effect desludging of the heat exchanger. During this time, the major portion of the operating medium flows from the economizer 32 through an opened valve 46' in a conduit 33' to a heat exchanger 34' and therefrom through a conduit 35 provided with an opened valve 47 into a superheater 37. The steam superheated in the superheater 37 flows through an open valve 51 in 'a conduit 39 as heating agent to the heat exchanger 34" and is conducted therefrom through a conduit 40 provided with a vlave 52, which is open at this time, to a final superheater 41, from which it is conducted to consumers, not shown. A valve 45' in a blow-down conduit 44' is closed. If the conversion zone in which water is converted into steam in the heat exchanger 34 must be desludged, supply of heating medium to this Zone is prevented by closing the valves 51 and 52' and liquid is flown from the economizer 32 through the conduit 33', the valve 46 being open, and through the conversion zone, the salts dissolved or suspended in the washing liquid being removed th ough the conduit 44', with the valve 45' being in open position. During the time the heat exchanger 3d is dcsludged, the operating medium is desalted in the heat exchanger 34, the valves 46, 47, 51, and 52 being open, and the blow-down valve 45 being closed. The alternate arrangement of the heat exchangers containing the conversion zones in the circuit of the operating medium affords uninterrupted operation of the steam generator with desalted operating medium.

Fig. 4 illustrates a modification of a plant according to Fig. 3. Washing-out of the conversion zones in the heat exchangers 34 and 34' is elfected by a washing fluid pumped from a reservoir 23 through a pump 24 either into conduit 20" and through a valve 19 into the dis-- charge conduit 35 of the conversion zone of the heat exchanger 34, or into a conduit 20 and through a valve 19 into the discharge conduit 35 of the conversion zone of the heat exchanger 34. In the first case, the valves 46, 47, 51 and 52 are closed and the liquid which has received the salts deposited in the conversion Zone of the heat exchanger 34 is removed from the conduit 33 through a blow-down valve 45" in a conduit 44". The left side of the plant shown in Fig. 4 continues to produce steam in the normal way. In the second case the valves 46, 47', 51 and 52 are closed and the desludging liquid is blown down through a valve 45 in a conduit 44 from the conduit 33'.

In the embodiments of the invention illustrated in Figs. 1 to 4, the conversion zone is arranged outside of the steam generator proper. It is important that these zones be protected against heat radiation and direct contact with burning fuel. It is, however, quite feasible to arrange the conversion zones within the steam generator, for example, in the flowof the combustion gases, it suitable precautions are taken. A plant of this type is shown in Fig. 5. The arrangement is similar to that shown in Fig. 2, the heat exchanger 4 which is heated by superheated steam being replaced by a tubular heater 57 which is heated, for example, by combustion gases. Normally the operating medium supplied by a pump 1 is preheated in an economizer 2, admitted through a valve 66 into a tube system 57 in which salts contained in the feed water are deposited and the liquid is converted into vapor which flows through a valve 67 into a superheater 61. For desludging the tube system 57, the valves 66 and 67 are closed and the liquid bypasses the conversion zone 57 through a conduit 58 in which a valve 68 has been opened. A limited amount of liquid can be vaporized and superheated in the superheater 61 during the relatively short desludging periods. Desludging liquid is pumped from a source of supply 23 by means of a pump 24 through a conduit 70 and a valve 69 into the tube system 57 and blown down therefrom through a valve 65.

The conversion zone may be heated in any other suitable manner, although heating according to the invention by means of desalted operating medium is of particular advantage. Tubular heat exchangers are preferably used in the performance of the method according to the invention.

While specific embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that various changes, modifications, substitutions, additions and omissions may be made therein without departing from the spirit and scope of the invention as set forth in flle appended claim.

What is claimed is:

The method of generating steam in a forced flow steam generator, particularly one operated at supercritical pressure, comprising heating water in a preheater, passing the preheated water, during normal operation, through an indirect heat exchanger for indirectly exchanging heat with superheated steam and thereby evaporating the water while the water passes through the heat exchanger, passing the steam produced in the heat exchanger through a superheater for superheating the steam, passing superheated steam from the superheater as heating agent through the heat exchanger, temporarily by-passing at least a portion of the preheated water around the heat exchanger and conducting the bypassed water directly to the superheater to be evaporated therein, conducting the balance of the preheated water through the heat exchanger for washing out salt deposits accumulated therein, blowing down all of the contaminated water which has been conducted through the heat exchanger, and simultaneously stopping flow of superheated steam through the heat exchanger.

References Cited in the file of this patent UNITED STATES PATENTS 2,488,598 Lockman Nov. 22, 1949 2,490,750 Grewin Dec. 6, 1949 2,647,570 Lockman Aug. 4, 1953 FOREIGN PATENTS 504,198 Belgium Oct. 24, 1952 20,466 Great Britain Feb. 8, 1912 382,731 Great Britain Nov. 3, 1932 95,805 Sweden May 30, 1939 

